/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#pragma once

#include "mongo/base/string_data.h"
#include "mongo/util/modules_incompletely_marked_header.h"

namespace mongo {

/**
 * Abstraction providing consistent `compare` and `hash_combine` operations for
 * use with polymorphic configurable sorting or to configure unordered
 * associative containers. These closely related operations are bundled into
 * this one interface.
 */
class MONGO_MOD_OPEN StringDataComparator {
public:
    virtual ~StringDataComparator() = default;

    /**
     * Compares two string values, applying a weak order (i.e. allowing ties).
     * Returns:
     *   <0 if `left < right`
     *    0 if `left == right`
     *   >0 if `left > right`
     */
    virtual int compare(StringData left, StringData right) const = 0;

    /**
     * Hash `str` in a way consistent with this comparator, storing the
     * result in the `seed` in-out parameter. Strings which `compare` equal
     * must have the same effect on all `seed` values.
     */
    virtual void hash_combine(size_t& seed, StringData str) const = 0;
};

/** Uses `StringData::compare` and Murmur3 hashing. */
class SimpleStringDataComparator final : public StringDataComparator {
public:
    constexpr int compare(StringData left, StringData right) const override {
        return left.compare(right);
    }

    void hash_combine(size_t& seed, StringData stringToHash) const override;
};

/** Singleton instance for use in basic string comparisons. */
inline const SimpleStringDataComparator simpleStringDataComparator{};

}  // namespace mongo
